Arterial smooth muscle will be studied to obtain information about the smooth muscle contractile system, to quantitate the physiological responses of the tissue, and to determine the contribution of smooth muscle to the mechanical properties of the arterial wall. The mechanical properties on isolated strips prepared from the media of hog carotid arteries give information on the passive and active stress-strain characteristics of elastic and contractile elements, and the relationship between load and velocity in this tissue. The relationship between the degree of activation of the smooth muscle and the mechanical properties of the strips is under investigation. Biochemical studies are directed towards determination of the contents of the various proteins of the contractile system and the properties of smooth muscle myosin, actin, and tropomyosin in comparison with their equivalents isolated from mammalian skeletal muscle. An x-ray diffraction study of the arterial strips is proposed to correlate length-tension data for the contractile system with reflections corresponsing to repeating longitudinal structures in an attempt to estimate filament lengths and the "sarcomere equivalent" of smooth muscle.